1. Field of the Invention
The present invention relates to a laminated glass for vehicle and, more particularly to a laminated glass for vehicle used in conjunction with an optical instrument.
2. Background Art
In order to enhance anti-glare and heat-shielding performance, some types of laminated glass for vehicle, particularly those for a windshield, are provided with a colored (green, blue, etc.) band-form shade area (i.e., shade band). Such a shade band is generally formed through coloring a band-form area of an intermediate film for joining glass sheets. By law, a windshield provided with a shade band is required to have an area (vision area) having a visible light transmittance equal to or higher than a predetermined value (e.g., ≧70%). Therefore, a shade band is generally formed in an upper section of a windshield, which is present outside the visible area.
In recent years, there has been proposed an intermediate film for laminated glass endowed with an IR-absorbing function for enhancing heat-shielding performance of window panes. This function is provided by dispersing particles of conductive material such as ITO (indium-doped tin oxide) in an intermediate film formed of a thermoplastic resin such as polyvinyl butyral (PVB) (see, for example, Japanese Patent Application Laid-Open (kokai) No. 8-259279).
Meanwhile, toward a recent trend for establishment of ITS (intelligent transport system) communication, a variety of instruments have come to be installed in a vehicle. Such instruments include a photoreceptor (e.g., a CCD camera), which is disposed so that light having a wavelength ranging from the visible region to the IR region is received via a glass pane, particularly via a windshield. When such an instrument is secured onto a windshield such that the instrument is in contact with the inner surface (i.e., the surface facing the interior of a vehicle) of the windshield, the instrument is preferably disposed in an upper section of the vision area of the windshield, so as to provide a sufficient vision area and to fully attain the function of the instrument.
However, as mentioned above, a shade band is often provided in an upper section of the windshield. Since the shade band considerably lowers the light transmittance within a range of visible light to IR light, the shade band reduces sensitivity of a provided photoreceptor to the light passing through the shade band.
Hitherto, in an attempt to solve the above problems, several methods have been proposed. For example, Japanese Patent Publication (kokoku) No. 48-81736 discloses a method of mitigating attenuation in transmittance through employment of an intermediate film formed of a plurality of layers not including a layer that reduces transmittance. The pamphlet of WO03/059837 discloses an approach including employing a low-transmission-loss intermediate film part instead of a part of a shade band causing high light transmission loss.
However, the method disclosed in Japanese Patent Publication (kokoku) No. 48-81736 has a drawback. Specifically, when a region of the shade band having higher visible-light transmittance is provided, the region of the intermediate film is formed in a dented shape. Thus, during the course of sticking with two glass sheets by such an intermediate film, complete degassing becomes difficult, and air bubbles remain in the space between the inner surfaces of the glass sheets. One possible approach for solving the problem is to fill, for planarization, the dented portion with a material having high transmittance. However, this approach is a cumbersome step, which is problematic. When the approach disclosed in the pamphlet of WO03/059837 is employed, a region of the intermediate film to be given higher transmittance must be substituted by a high-transmittance intermediate film part, which is also a problematically cumbersome step.
Japanese Patent Application Laid-Open (kokai) No. 2002-173347 discloses a laminated glass employing an intermediate film containing IR-shielding microparticles which provide small transmission loss in terms of infrared light having a wavelength of about 850 nm. The infrared light is employed in a system such as a VICS (vehicle information and communication system) or a key-less entry system installed in a vehicle. However, when the method disclosed in Japanese Patent Application Laid-Open (kokai) No. 2002-173347 is employed, IR-shielding microparticles contained in the intermediate film make the near-IR (750 to 1,000 nm) light transmittance poor. Thus, such a laminated glass is not preferred for a case where an optical instrument employing light having a wavelength falling within the near-IR range is provided on the inner surface of the glass pane.
In addition, a pigment employed as a colorant for producing a conventional shade lowers the near-IR (750 to 1,000 nm) light transmittance. Thus, when such a pigment is employed, near-IR light cannot completely be received, in the case where an optical instrument employing near-IR light is provided on the interior surface of the glass pane.